Performance issues - Slow Zoom when using the Zoom command

I'm having performance issue when using the zoom command with 2006 when in model space. Using the wheel you can zoom and pan normally. When using the zoom command itself you get a hesitating zoom (like slow motion) whether zooming in or out either way. I've checked the viewres command for fast zooms and turned on regenauto feature. Makes no difference.

When in a Layout view it zooms normally. Size of drawing makes no difference. Never had this issue with any previous version.

It's a new feature in A2006. Set the variable VTENABLE to 0 to stop it.

Thanks. Appreciate the help.